Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$169.32	11.170%	$188.233	$188.23	$188.25	$188.20
Purchase #2	$118.51	4.384%	$123.7055	$123.71	$123.70	$123.70
Purchase #3	$141.50	11.612%	$157.931	$157.93	$157.95	$157.90
Purchase #4	$104.88	6.600%	$111.8021	$111.80	$111.80	$111.80
Purchase #5	$105.40	13.848%	$119.9958	$120.00	$120.00	$120.00
Purchase #6	$108.95	5.161%	$114.5729	$114.57	$114.55	$114.60
Purchase #7	$30.32	4.676%	$31.7378	$31.74	$31.75	$31.70
7 purchase totals =	$778.88		$847.9781	$847.98	$848.00	$847.90